The exact cause of 'Devil Comet' 12P/Pons-Brooks' flare-ups is unknown, though the best guess is that perhaps a fissure has developed on the comet's nucleus due to a build-up of gas.

'Devil Comet' 12P/Pons-Brooks is approaching Earth. Why is it flaring up, 'horns' and all?

Source: space
Source Link: https://www.space.com/devil-comet-12p-pons-brooks-approaching-earth